UNIVERSITY    OF     CALIFORNIA      AGRICULTURAL  EXPERIMENT  STATION 

BENJ.    IDE    WHEE.LER,    President 

COLLEGE    OF    AGRICULTURE  thomas   forsyth    hunt,  dean  and  director 

H.      E.      VAN     NORMAN         VICE- DlR ECTOR      AND       DEAN 

BERKELEY  university    FarmSchool 

CIRCULAR  No.  136 

(August,   1915) 

MELILOTUS    INDICA    AS    A    GREEN    MANURE 
CROP    IN    SOUTHERN    CALIFORNIA* 

By  W.   M.  MEETZ 


Melilotus  indica,  or  bitter  clover,1  will  make  a  satisfactory  develop- 
ment during  the  cool  winter  months  of  southern  California. 

It  has  outyielded  common  vetch  and  Canadian  field  peas,  the  two 
legumes  most  generally  used  in  the  past. 

It  has  increased  the  yield  of  the  crops  following  its  incorporation 
in  the  soil,  to  a  greater  extent  than  any  of  the  other  legumes  tested. 

It  is  practically  immune  to  aphis  injury  and  will  stand  more  frost 
than  either  vetch  or  peas. 

It  starts  slowly  and  must  be  planted  not  later  than  October 
fifteenth  if  it  is  to  be  plowed  under  by  March. 

The  seed  of  this  clover  is  now  largely  a  by-product,  being  separated 
from  the  screenings  of  wheat  in  which  it  is  often  a  prevalent  weed. 
It  is  a  heavy  seed  producer,  and  should  the  supply  from  the  above 
mentioned  source  be  insufficient,  it  could  be  grown  as  a  seed  crop  at 
a  cost  much  below  that  of  most  other  clovers. 

At  the  present  writing,  good  recleaned  seed  can  be  obtained  at 
from  7  to  10  cents  per  pound.  This  makes  the  seed  cost  less  per 
acre  than  vetch  or  peas. 

Per  acre,     25  pounds,  M.  indica,  at  10c $2.50 

Per  acre,     75  pounds,  Common  vetch,  at  4c 3.00 

Per  acre,  100  pounds,  Canadian  peas,  at  4c 4.00 

In  the  southwest,  especially  in  Arizona  and  California  a  yellow 
flowering  annual  species  of  Melilotus  is  found  growing  wild  under 
widely  differing  climatic  and  soil  environments.  This  species,  Melilotus 
indica,  has  been  looked  upon  as  a  pest  in  many  sections  where  it  is 
a  prevalent  weed  in  grain  fields.  Recently,  however,  this  crop  has 
proved  to  be  well  adapted  for  growing  in  the  winter  as  a  green- 
manuring  crop  and  has  been  used  to  a  limited  extent  in  the  citrus 
orchards  both  in  California  and  Arizona. 

Melilotus  indica  is  the  only  one  of  the  three  common  species  of 
Melilotus  that  will  make  a  satisfactory  winter  growth  under  California 

*  Paper  No.  8,  Citrus  Experiment  Station,  College  of  Agriculture,  Univer- 
sity of  California,  Eiverside,  California. 

1  Melilotus  indica  is  variously  known  as  bitter  clover;  yellow  top,  sour  clover, 
and  siceet  clover.  The  latter  term  has  been  applied  so  generally  to  Melilotus 
alba  that  its  use  in  this  connection  is  confusing.  If  a  commercial  term  is 
necessary  the  name  bitter  clover  seems  to  be  the  most  descriptive  of  those  now 
in  use,  since  the  taste  of  both  seed  and  stem  is  decidedly  bitter. 


conditions.  M.  alba  makes  a  good  summer  growth  and  under  con- 
ditions where  the  growing  of  a  summer  green  manure  crop  is  feasible, 
this  sweet  clover  seems  to  be  superior  to  cow  peas,  buckwheat,  or 
soja  beans. 

During  the  past  winter,  1914-15,  M.  indica  was  grown  to  a  con- 
siderable extent  in  practically  all  of  the  citrus  sections  of  California. 
Reports  have  been  received  from  all  parts  of  the  state  telling  of  success 
with  this  new  cover-crop,  and  the  writer  has  seen  heavy  tonnages  of 
it  produced  on  most  of  the  soil  types  common  to  southern  California, 
from  the  cobble  stone  soil  of  canyon  washes  to  the  stiffest  of  clay  adobes. 


EXPERIMENTS  WITH  M.  INDICA   AS  A  GREEN  MANURE  CROP 

For  the  past  five  years,  M.  indica  has  been  tested  as  a  green  manure 
crop  at  the  Citrus  Experiment  Station  and  has  uniformly  given  very 
satisfactory  results.  From  the  start  this  crop  gave  good  tonnages  of 
organic  material,  and  in  the  yields  of  the  crops  following  it,  marked  in- 
creases were  obtained.  In  this  series  of  experiments,  tenth  acre  plats 
were  used,  there  being  a  total  of  seventeen  plats.  On  nine  plats  different 
legumes  Avere  used  as  winter  cover-crops.  On  every  alternate  plat  a 
non-legume,  rye  or  barley,  was  used  as  a  winter  cover-crop,  these  being 
check  plats  in  comparison  with  the  legumes.  All  of  the  green  manure 
crops  are  sown  during  September  and  turned  under  early  in  the  spring, 
either  in  February  or  in  March.  Irrigations  at  monthly  intervals  are 
given  these  crops  until  the  winter  rains  begin.  After  plowing  under 
the  winter  cover-crops  on  the  different  plats,  various  field  crops,  as 
potatoes,  corn,  or  sugar  beets,  are  planted  over  the  area  as  indicators 
of  the  comparative  value  of  the  different  cover-crops  as  green  manures. 
An  equal-sized  plat  of  these  field  crops  is  grown  on  each  of  the  seven- 
teen green  manure  plats.  Uniform  cultivations  and  irrigations  are 
given  all  plats.  At  maturity  the  various  crops  are  harvested,  and 
accurate  weighings  made  of  the  yields  of  each  plat.  In  a  comparison 
of  these  nine  legume  plats  with  the  cereal  plats,  the  effects  on  the  crop 
following  the  incorporation  of  these  green  manures  were  quite  varied. 

In  every  case,  the  crops,  following  the  incorporation  of  the  legumes, 
gave  yields  much  in  excess  of  those  grown  after  a  cereal  crop  had 
been  turned  under.  There  was  also  a  considerable  difference  in  the 
effect  of  the  various  legumes.  The  common  vetch,  Vicia  sativa,  which 
has  been  more  extensively  used  for  green  manuring  than  any  other 
legume,  gave  a  much  less  marked  increase  in  yield  in  the  test  crops 
following  it  than  several  of  the  other  less  common  legumes.  Taking 
the  non-legume  plats  as  checks,  Melilotus  indica,  as  a  green  manure, 
resulted  in  an  average  increase  in  yield  of  the  test  crops  following 
it  of  64.8  per  cent,  while  common  vetch,  V.  sativa,  gave  only  28.7  per 
cent,  bur  clover,  Medicago  denticulata,  30.4  per  cent,  and  Canadian 
peas,  Pisum  arvense,  43.3  per  cent.2 

2  Six  different  field  crops  were  used  in  determining  these  increases,  and  in 
all,  fifteen  crops  were  averaged  in  getting  the  percentages  of  increase  in  the 
yield  given  here. 


Iii  this  experiment  four  of  the  eight  cereal  plats  had  applied  to 
them  different  amounts  of  nitrogenous  fertilizers  in  the  form  of  nitrate 
of  soda  or  dried  blood.  In  one  case  the  application  was  at  the  rate 
of  1092  pounds  of  nitrate  of  soda  or  1188  pounds  of  dried  blood  per 
acre.  The  effect  of  this  addition  of  nitrogen  was  very  noticeable  with 
all  the  field  crops.  Even  after  applying  this  heavy  application  of 
nitrogen  in  addition  to  the  green  manure  crop  of  rye  or  barley,  the 
average  percentage  of  increase  in  the  field  crops  following  was  only 
45.6  per  cent  or  fully  one-third  less  than  that  obtained  from  the  use 
of  a  green  manure  crop  of  Melilotus  indica  without  further  nitrogen 
additions  of  any  sort. 

The  average  tonnage  of  green  tops  produced  by  this  melilotus  clover 
has  always  compared  favorably  with  any  of  the  other  crops  grown, 
either  legumes  or  cereals.  The  root  system  of  this  plant,  however,  is 
much  larger  than  that  of  the  vetches  or  peas.  A  deep  tap-root  is 
characteristic  of  all  melilotus  clovers,  and  although  this  species  is  an 
annual,  it  is  no  exception  in  this  regard.  In  fact,  six-months-old  plants 
have  shown  tap-roots  penetrating  to  a  depth  of  eight  feet  under 
ordinary  orchard  conditions. 

Most  of  the  orchard  soils  in  southern  California  have  a  tendency 
to  form  a  plow  sole  or  irrigation  hardpan.  This  is  commonly  con- 
sidered to  be  caused  in  large  measure  by  the  frequent  cultivations 
and  irrigations.  The  frequent  stirring  of  the  dry  pulverized  soil, 
together  with  frequent  applications  of  water,  tends  to  sift  out  and 
wash  down  the  finer  clay  particles  and  deposit  them  in  a  dense 
hard  layer  of  varying  thickness,  just  under  the  cultivated  area.  Cul- 
tivating the  soil  when  it  is  too  wet  or  too  dry  tends  to  change  the 
physical  condition  of  the  clay  and  make  this  hardpan  condition  worse. 
Much  can  be  done  toward  bettering  this  condition  through  proper 
methods  of  the  cultivations,  but  even  under  the  best  of  conditions  many 
of  our  soils  become  more  or  less  impervious  to  water  if  something  is 
not  done  to  open  up  this  compact  layer.  Nothing  seems  to  do  this  as 
satisfactorily  as  do  roots  of  rapid-growing,  deep-rooted  plants.  Our 
experience  has  shown  that  the  difference  in  the  time  necessary  to  wet 
the  soil  to  a  depth  of  four  feet  is  very  marked  between  plats  having 
no  green-manure  crop  and  those  growing  each  winter  a  crop  of  M. 
indica  or  vetch.  For  this  purpose,  M.  indica  is  superior  to  any  of 
the  other  winter-growing  legumes  now  available. 

TIME,   RATE,    AND    METHOD    OF    SEEDING 

Under  orchard  conditions  in  the  citrus  sections  where  it  is  ordinarily 
thought  highly  advisable  to  plow  early,  that  is,  during  February  and 
March,  it  is  necessary  to  sow  M.  indica  not  later  than  the  middle  of 
October  if  a  satisfactory  growth  is  to  be  had  by  plowing  time.  In 
walnuts  and  other  irrigated,  deciduous  orchards,  where  it  is  considered 
possible  to  plow  later  without  injury,  the  planting  of  this  bitter  clover 
as  late  as  December  15th  has  given  very  satisfactory  results.  The 
rate  of  seeding  depends  upon  two  factors — the  actual  area  of  land 
planted  and  the  quality  of  the  seed  sown. 


At  present,  the  seed  of  M.  indica  is  largely  obtained  from  the  screen- 
ings of  wheat,  and  unless  thoroughly  recleaned  is  apt  to  contain  much 
weed  seed  and  considerable  immature  seed.  Many  samples  of  this 
seed  also  show  from  5  to  20  per  cent  of  hard  seeds  which  do  not  germin- 
ate the  first  season.  For  these  reasons  the  quantity  of  seed  recom- 
mended is  greater  than  would  be  necessary  with  seed  of  high  quality. 
The  best  results  have  usually  followed  the  sowing  of  from  20  to  35 
pounds  of  seed  per  acre,  when  practically  all  the  land  is  planted,  the 
amount  per  acre  to  be  reduced  as  the  trees  take  up  appreciable  space. 
Experience  has  shown  that  in  most  cases  much  better  results  are  ob- 
tained when  the  seed  is  sown  on  the  dry  soil-mulch  before  irrigating 
rather  than  in  the  moist  soil  just  after  irrigation,  as  is  the  common 
practice  with  vetches  and  peas. 

The  seed  is  very  small  and  under  orchard  conditions  should  be 
sown  broadcast  and  then  lightly  cultivated  or  harrowed  into  the  soil. 
The  irrigation  furrows  should  then  be  made  close  enough  together 
to  permit  of  as  complete  a  wetting  of  the  surface  as  possible.  This 
is  necessary  if  a  uniform  stand  is  to  be  obtained  over  all  the  land. 
Otherwise,  much  of  the  seed  will  not  germinate  until  the  rains  begin. 
On  very  fine  sandy  soil  good  results  have-  followed  sowing  the  seed 
after  an  irrigation  and  then  cultivating  it  in  while  the  surface  soil  is 
still  quite  moist.  On  all  other  types  of  soil  this  method  has  never  given 
good  results. 


INOCULATION 

All  legumes  have  the  power  of  taking  nitrogen  from  the  air 
indirectly  through  the  bacteria  which  are  naturally  present  in  the 
nodules  on  the  roots  of  this  group  of  plants.  Under  cultivation,  how- 
ever, many  such  plants  are  sown  on  soil  new  to  the  plant  and  in  which 
the  necessary  species  of  bacteria  may  be  absent.  Most  legumes  will 
develop  to  a  fair  degree  without  the  assistance  of  the  bacteria,  but  all 
grow  better  with  the  added  supply  of  nitrogen  which  these  tiny 
organisms  make  available  to  them.  When  legumes  are  used  as  soiling 
crops,  it  is  necessary  to  have  good  inoculation  of  the  plant  roots  if  any 
considerable  amount  of  nitrogen  is  to  be  added  to  the  soil  through  the 
decay  of  these  crops.  Melilotus  indica  grows  wild  over  much  of  the 
state  and  is  in  this  wild  condition  naturally  well  inoculated. 

The  bacteria  that  are  found  in  the  nodules  on  the  roots  of  the 
common  bur  clover,  Medicago  denticidata,  are  the  same  species  as 
that  which  inoculates  the  sweet  clovers  and  alfalfa.  For  this  reason, 
many  of  our  soils  do  not  need  further  inoculation  to  grow  Melilotus 
indica  and  to  insure  the  addition  of  the  maximum  amount  of  nitrogen 
from  the  air.  There  are,  however,  many  orchard  soils  that  have  been 
clean  cultivated  for  so  long  a  time  that  these  organisms  may  not  be 
presenl  in  sufficient  numbers.  On  such  soils  artificial  inoculation  is 
desirable. 

Directions  for  inexpensive  inoculation  are  given  in  Circular  No.  87 
of  this  Experiment  Station,  on  "Alfalfa." 


